The present invention relates to the field of electrophotography. More particularly, it relates to improvements in electrophotographic copiers of the type which incorporate an automatic document feeder, a multibin sorter, and an "accent" or "spot" color feature by which, for example, certain selected document information can be color highlighted with respect to other document information on a copy sheet.
Electrophotographic document copiers are well known in the art. Many of them, especially those designed for high volume copying, include an automatic document feeder for serially presenting the individual pages of a multipage document to be copied to the exposure platen of the copier. Some of these copiers also include a multibin sorter for accumulating collated, multisheet copies or "sets" of the multipage original document.
In copiers having both a document feeder and a sorter attachment, the copier normally "defaults" to a "recirculation" mode in which the document feeder repeatedly circulates the individual pages of the multipage original, one page at a time, between a document supply tray and the exposure platen of the copier. In this mode, the copier's image recording section cooperates with said document feeder to produce a collated, multisheet copy of the multipage document for each circulation of the multipage document and to deliver such copies, one atop the other, to an external exit hopper.
In addition to the aforementioned "recirculation" mode, document copiers of the above type can be selectively operated in a "non-recirculation" or "sorter" mode, in which case the document feeder, upon presenting a document page to the copier's exposure platen, operates to maintain such page on the exposure platen while multiple exposures are made. The copier's image recording section produces and delivers one copy of each document page to a discrete bin of the sorter. In this manner, the feeder cooperates with the image recording section to produce a collated, multisheet copy of a multipage document in each of the bins comprising the multibin sorter.
As between the two modes of operation described above, the "recirculation" mode is usually the more preferred mode since, in the majority of copying jobs, the original document consists of a relatively small number of pages, e.g., less than twenty, and the operator usually prefers to receive the collated copies in a single output tray, rather than in a plurality of separate bins. Note, in either mode, the feeder can usually present one or both sides of each document page to the exposure platen for copying.
In U.S. Pat. Nos. 4,740,818 (Tsilibes et al.) and 4,963,932 (Horwath), there is disclosed document-editing apparatus by which a copier operator can, by means of an editing stylus or wand, designate certain pages or page portions of a multipage original which are to receive certain "special" treatment during the copying process. Such treatment may include, for example, the use of "accent" or "spot" color to highlight certain text or graphic information, or the use of a half-tone screen or special development bias to increase or decrease the contrast or density of selected portions of the image. The copier's logic and control (LCU) responds to the output of the editing apparatus, which indicates the page number and special treatment to be given to a particular document page, and adjusts the copying process accordingly.
U.S. Pat. No. 4,775,510 (M. J. Russel) discloses an electrophotographic document copier of the type which includes both a document feeder and apparatus for providing accent or spot color. In one embodiment, this copier uses an intermediate storage tray to temporarily store one or more copy sheets between successive presentations to an image transfer station where, during a first pass, a copy sheet first receives a toner image of one color and, during a second pass, receives a toner image of a different color. Upon receiving images of two different colors, the copy sheets are delivered to an "accessory unit" which, though not specifically mentioned, could be a multibin sorter.
To automatically produce multiple copies of a multipage original in which one or more pages is to be copied with accent color, the above-mentioned Russel copier could operate in either of two modes. In a recirculation mode, the copier would operate to serially present each original page to the copier's exposure platen for copying. While feeding those original pages that require no special treatment (i.e., no accent color), the copier operates in its normal fashion, making one copy of each original page presented to the copier's exposure station, and delivering the copy sheet to an external exit hopper. When, however, a document page requiring accent color is presented to the exposure platen, the feeder will allow such page to remain on the platen while two successive latent images are formed on the copier's recording element. Prior to developing the first image with toner of a first color (e.g., black), that portion of the image which is to be developed with an accent color (e.g., red toner) is selectively erased from the recording element. Similarly, before developing the second image with toner of the accent color, that portion of the image which is not to receive the accent color is erased. In order for one copy sheet to receive both of these toner images, the copy sheet feeding apparatus will feed the copy sheet from the image transfer station (where it received the first toner image), along an endless path leading through the intermediate storage tray and back to the transfer station so that it may receive the accent color image. Because this endless path is of such length that it requires several copy sheets to fill, there must be a suitable time delay between the formation of the two related successive images on the recording element. Typically, several image frames on the recording element will be skipped between these two images. This requirement for multiple "skip frames" each time a document page is encountered that requires accent color (or, for that matter, any other treatment that requires two presentations of the copy sheet to an image transfer station) translates to an inefficiency in the copying process, causing the copier to produce copies at less than full machine speed.
Rather than operating in a "recirculation" mode, the above copier of Russel might operate in a "sorter" mode in making multiple copies of the multipage original described. In this mode, each original page remains on the exposure platen until the requisite number of copies are made, and the copies of each different page are delivered to different bins. When a page requiring accent color is encountered, all copies of the first transferred image are delivered to the intermediate storage tray where they are temporarily stored until the time comes to receive the accent color image, whereupon they are returned to the copier's transfer station. When the number of copies desired is such that the endless path leading from the transfer station, through the intermediate tray and back to the transfer station is filled with copy sheets, there is no need for multiple skip frames, and the copier can operate at near full machine speed.
While the number of skip frames can be reduced by operating the copier described above in a "sorter" mode, the recognition of this fact is not readily apparent to the casual operator. Since, as noted above, copiers of this type will normally default to a "recirculation" mode unless instructed otherwise, there is a latent inefficiency in such copiers when confronted with a copying job of the type described.
From the foregoing discussion, an object of this invention is to overcome the latent inefficiency in using a copier of the above type to produce multiple collated copies of a multipage document in which at least one document page must be cycled past an image transfer station twice in order to complete a copying operation.